1. Field of the Invention
The invention relates to a process for the synthesis of polymers with laterally linked polyoxyalkylene chains by the free radical polymerization of polyoxyalkylene ethers with olefinic double bonds with other vinyl compounds, capable of copolymerizing, and the use of such polymers for the production of polyurethanes.
2. Description of the Prior Art
Polymers with laterally linked long-chain radicals have proven to be very effective surface-active compounds. Polysiloxanes with laterally linked polyoxyalkylene chains are used as foam stabilizers in the production of polyurethane foams. Depending on their hydrophilic/hydrophobic balance, they can also be used as emulsifiers or as emulsion breakers, as well as for preventing or eliminating foam in aqueous or organic systems.
Polymers with laterally linked polyalkylene oxide chains, which can be synthesized by reacting polyalkylene oxides having at least two free hydroxyl groups on the starting alcohol with compounds which are di- or polyfunctional with respect to the hydroxyl groups on the starting alcohol, are described in German patent application No. P 31 09 700.6. Optionally, these reactions may be carried out in the presence of solvents and/or catalysts and/or elevated temperatures. The compounds are further distinguished by a high surface activity and have a relatively low viscosity even at higher molecular weights.
It is furthermore known that polymers with laterally linked polyalkylene oxide chains can be synthesized by the free radical polymerization of polyoxyalkylene ethers having olefinic double bonds in the starting alcohol. For example, partial esterification of alkylene glycol with acrylic acid and the addition of alkylene oxide to the free OH groups is known from the journal "Plaste und Kautschuk" (28, Volume 7, 1981, page 367). The compounds so obtained can be polymerized in the presence of other monomeric compounds suitable for polymerization to form polymers with laterally linked polyoxyalkylene chains. These compounds, however, have the disadvantage that they can be saponified in acidic or alkaline media, the laterally linked polyoxyalkylene chains being split off.
The alkoxylation products of copolymers of allyl alcohol and alkenyl aromatic compounds and their use in the production of lacquers and foams based on polyurethanes is described in U.S. Pat. No. 2,965,615. The large amount of unreacted allyl alcohol remaining after the reaction which results from unfavorable polymerization parameters, the necessary removal of the solvents required for carrying out the free radical polymerization after the alkoxylation, and the high viscosity of the products of the process, are disadvantages of this process.
A process for copolymerizing polyoxyethylene ethers of allyl alcohol with acrylic or methacrylic acid or their salts is described in Japanese patent publication No. 81 81 320. However, on repeating this process, it turns out that either gelling takes place during the polymerization because of crosslinking by way of principal valence bonds or polymers with only a low molecular weight are obtained.
Dispersions of graft copolymers which are synthesized from vinyl monomers and polyetherols and which are used for the production of polyurethanes, are described in U.S. Pat. Nos. 3,383,351 and 3,652,639. The polyols used in accordance with the first mentioned patent, are completely free of ethylenic double bonds. It is noted that the presence of ethylenic double bonds favors the formation of crosslinking bridges and, in so doing, increases the viscosity of the dispersions formed in an undesirable manner. It is a significant disadvantage of the process of U.S. Pat. No. 3,383,351 that the stable dispersions prepared from numerous customary vinyl monomers, such as, styrene, cannot be processed if these monomers are used in an amount sufficient to impart the desired mechanical strength to polyurethanes. On the other hand, it is noted in U.S. Pat. No. 3,652,639 that homogeneous graft copolymers based on acrylonitrile can be synthesized in liquid media by the in situ polymerization of acrylonitrile with an unsaturated polyol, in the presence of a catalyst which forms free radicals. The polyols used as described in U.S. Pat. No. 3,652,639, contain at least about 1 mole of unsaturated units per mole of polyol. A disadvantage of these products is their relatively high viscosity, which can be attributed to the presence of graft copolymers of extremely small particle size and to the formation of crosslinking bridges.
German patent No. 2 359 617 relates to dispersions of graft copolymers which are prepared by polymerizing a vinyl monomer in situ in the presence of a free radical forming catalyst in a polyetherol, which contains 0.1 to 0.7 moles of unsaturated units per mole of polyetherol. It is a significant disadvantage of this process that, unless a high viscosity or crosslinking of products of the reaction is acceptable, the ratio of unsaturated to saturated polyetherols cannot exceed an upper limit. The reason for this is that, because of statistical distribution, the unsaturated polyetherols described may also carry several unsaturated double bonds in one molecule. Therefore, quite highly viscous, cloudy and even gelled products may be formed in free radical graft copolymerization at the upper range of the ratio given.